c7E3 Fab Research Articles

Abciximab-induced acute profound thrombocytopenia postpercutaneous coronary intervention

Abciximab (c7E3 Fab) is one of the three potent intravenous glycoprotein IIb/IIIa receptor inhibitors (along with eptifibatide and tirofiban) that have shown significant positive outcomes when used in patients with...

Clot-On-A-Chip: A Microfluidic Device To Study Platelet Aggregation and Contractility Under Shear

IntroductionIn primary hemostasis, platelets adhere, activate, and aggregate at the wall of an injured vessel to form a hemostatic plug for the cessation of bleeding. After activation, platelets generate myosin-driven contractile forces to compact the size of the plug in order to reduce the space between platelets and prevent their disaggregation. Hemodynamic shear can be a major effector of platelet function in hemostasis, but its effect on the ability of platelets to produce contractile forces is an open question. Studying the dynamics of platelet aggregation and platelet force generation under hemodynamic shear can provide important insights into hemostasis and thrombosis. MethodWe have developed a microfluidic device that uses microscale blocks to induce platelet aggregation and microscale posts to measure platelet forces in a hemostatic plug. Whole human blood in heparin or citrate is pumped through a microfabricated chip containing microchannels with arrays of blocks and posts arranged along the bottom of a microchannel (Fig. 1). The surface of the blocks and posts are pre-coated with von Willebrand factor and type I collagen to allow for platelet adhesion. As blood is passes over a block, its rectangular shape induces a high shear rate that causes platelets to aggregate on its surface. A flexible micropost is situated behind each block. As platelets aggregate between the block and post, their contractile forces causes the post to bend toward the block. The deflection of the post is recorded under fluorescence microscopy and analyzed using quantitative image analysis of the videos. Since a microscale post bends like a cantilever beam, its deflection can be used to quantify the forces of platelets. ResultsBlebbistatin, a myosin inhibitor, was used to confirm that deflection of the posts by the platelets in heparinized blood was due to myosin activity. When blood was incubated with 2-MeSAMP, a P2Y12 antagonist, platelets were able to aggregate, but their ability to generate contractile forces was substantially reduced. This finding indicates that ADP activation is needed for platelet contractility under shear. The rate of hemodynamic shear was found to influence platelet function, for the rate of platelet aggregation and force generation were found to increase for blood sheared from 2000 to 12,000 s-1. Moreover, platelet aggregation and contractile forces were reduced when glycoprotein Ib-V-IX complex and integrin αIIbβ3 were inhibited with antibody AK2 and antibody fragment c7E3 Fab, respectively. When citrated blood was incubated with tissue plasminogen activator, platelets aggregate and produced contractile forces that increased steadily within the first ten minutes, but then the forces began to subside. ConclusionsOur device can be used to study the role of hemodynamic shear in platelet function and gives insights into the role of platelet forces during hemostasis. Its microscale dimensions also allow us the study the biomechanics involved in the formation of a hemostatic plug during its early stages of growth and stability. [Display omitted] Disclosures:White:Vidacare Corp: Honoraria; Stasys Medical Corp: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties; NIH: Research Funding; Coulter Foundation: Research Funding; Washington State Life Sciences Discovery Fund: Research Funding. Sniadecki:Stasys Medical Corporation: Equity Ownership, Founder Other, Membership on an entity's Board of Directors or advisory committees.

Phosphoinositide 3-Kinase p110β Regulates Integrin αIIbβ3 Avidity and the Cellular Transmission of Contractile Forces

Phosphoinositide (PI) 3-kinase (PI3K) signaling processes play an important role in regulating the adhesive function of integrin alpha(IIb)beta(3), necessary for platelet spreading and sustained platelet aggregation. PI3K inhibitors are effective at reducing platelet aggregation and thrombus formation in vivo and as a consequence are currently being evaluated as novel antithrombotic agents. PI3K regulation of integrin alpha(IIb)beta(3) activation (affinity modulation) primarily occurs downstream of G(i)-coupled and tyrosine kinase-linked receptors linked to the activation of Rap1b, AKT, and phospholipase C. In the present study, we demonstrate an important role for PI3Ks in regulating the avidity (strength of adhesion) of high affinity integrin alpha(IIb)beta(3) bonds, necessary for the cellular transmission of contractile forces. Using knock-out mouse models and isoform-selective PI3K inhibitors, we demonstrate that the Type Ia p110 beta isoform plays a major role in regulating thrombin-stimulated fibrin clot retraction in vitro. Reduced clot retraction induced by PI3K inhibitors was not associated with defects in integrin alpha(IIb)beta(3) activation, actin polymerization, or actomyosin contractility but was associated with a defect in integrin alpha(IIb)beta(3) association with the contractile cytoskeleton. Analysis of integrin alpha(IIb)beta(3) adhesion contacts using total internal reflection fluorescence microscopy revealed an important role for PI3Ks in regulating the stability of high affinity integrin alpha(IIb)beta(3) bonds. These studies demonstrate an important role for PI3K p110 beta in regulating the avidity of high affinity integrin alpha(IIb)beta(3) receptors, necessary for the cellular transmission of contractile forces. These findings may provide new insight into the potential antithrombotic properties of PI3K p110 beta inhibitors.

Eptifibatide and abciximab inhibit insulin-induced focal adhesion formation and proliferative responses in human aortic smooth muscle cells

BackgroundThe use of abciximab (c7E3 Fab) or eptifibatide improves clinical outcomes in diabetics undergoing percutaneous coronary intervention. These β3 integrin inhibitors antagonize fibrinogen binding to αIIbβ3 integrins on platelets and ligand binding to αvβ3 integrins on vascular cells. αvβ3 integrins influence responses to insulin in various cell types but effects in human aortic smooth muscle cells (HASMC) are unknown.Results and discussionInsulin elicited a dose-dependent proliferative response in HASMC. Pretreatment with m7E3 (an anti-β3 integrin monoclonal antibody from which abciximab is derived), c7E3 or LM609 inhibited proliferative responses to insulin by 81%, 59% and 28%, respectively. Eptifibatide or cyclic RGD peptides completely abolished insulin-induced proliferation whereas tirofiban, which binds αIIbβ3 but not αvβ3, had no effect. Insulin-induced increases in c-Jun NH2-terminal kinase-1 (JNK1) activity were partially inhibited by m7E3 and eptifibatide whereas antagonism of αvβ3 integrins had no effect on insulin-induced increases in extracellular signal-regulated kinase (ERK) activity. Insulin stimulated a rapid increase in the number of vinculin-containing focal adhesions per cell and treatment with m7E3, c7E3 or eptifibatide inhibited insulin-induced increases in focal adhesions by 100%, 74% and 73%, respectively.ConclusionThese results demonstrate that αvβ3 antagonists inhibit signaling, focal adhesion formation and proliferation of insulin-treated HASMC.

Efficacy of Abciximab for Patients Undergoing Balloon Angioplasty Data From Japanese Evaluation of c7E3 Fab for Elective and Primary PCI Organization in Randomized Trial (JEPPORT)

The efficacy and safety of abciximab were investigated in Japanese patients undergoing percutaneous coronary intervention (PCI) for acute myocardial infarction (MI) or unstable angina. The 973 patients were randomized into 3 groups: the low-dose group (L group) received bolus injection of 0.20 mg/kg followed by 12-h infusion; the high-dose group (H group) received bolus injection of 0.25 mg/kg followed by 12-h infusion; the placebo group (P group) received bolus and infusion of placebo. The incidence of the primary endpoint (30-day post-PCI coronary events: death, MI or urgent revascularization) was 3.6%, 1.6%, and 4.1% in the P, L, and H groups, respectively, with no significant difference between the P and L groups (P=0.104) or between the P and H groups (P=0.772). The incidence of bleeding tended to increase in a dose-dependent manner. No significant difference in the incidence of coronary events was found between the placebo and abciximab groups, so the efficacy of abciximab in preventing post-PCI coronary events in Japanese patients was not confirmed.

C7E3 Fab inhibits human tumor angiogenesis in a SCID mouse human skin xenograft model

The alphavbeta3 integrin plays an important role in tumor growth and angiogenesis. Inhibition of this receptor by intact bivalent antibodies has been shown to inhibit angiogenesis and tumor growth. In this study we tested the chimeric Fab of 7E3 (c7E3 Fab), an antibody reactive with human platelet GPIIb/IIIa and alphavbeta3 to determine if it would inhibit in vivo angiogenesis and tumor growth in a SCID mouse/human skin tumor growth and angiogenesis model. c7E3 Fab inhibited human tumor angiogenesis and tumor growth. These data suggest monovalent antibody fragments devoid of antibody effector function can have efficacy in preclinical models of angiogenesis.

Elevated Placental Growth Factor Levels Are Associated With Adverse Outcomes at Four-Year Follow-Up in Patients With Acute Coronary Syndromes

This study sought to evaluate the predictive value of baseline placental growth factor (PlGF) for long-term cardiovascular events in acute coronary syndromes (ACS). A biomarker of vascular inflammation, PlGF is identified as a powerful predictor for short-term outcome in patients with ACS. In 544 patients who were enrolled in the placebo arm of the c7E3 Fab Anti Platelet Therapy in Unstable REfractory angina (CAPTURE) trial, PlGF levels were determined as well as markers of myocardial necrosis (troponin T [TnT]), general inflammation (high-sensitivity C-reactive protein [hsCRP]), and platelet activation (soluble CD40 ligand [sCD40L]). Cox proportional hazard regression analyses were applied to evaluate the relationship between biomarkers and the occurrence of all-cause death or non-fatal myocardial infarction during a median follow-up period of four years. Patients with PlGF levels in the fourth and fifth quintile (>27 ng/l) had higher mortality than those with lower levels (10.8% vs. 3.2%; hazard ratio [HR], 3.3; 95% confidence interval [CI], 1.6 to 7.1), as well as a higher incidence of the composite end point of death or myocardial infarction (27.6% vs. 11.3% events; HR, 2.6; 95% CI, 1.7 to 3.9). The relationship between PlGF and the composite end point remained significant after adjustment for TnT, sCD40L, and hsCRP (adjusted HR, 3.3; 95% CI, 2.0 to 5.4). In patients with ACS, elevated plasma levels of PlGF are associated with adverse cardiac outcomes during long-term follow-up. These data suggest that PlGF as a more specific marker of vascular inflammation should be considered for risk stratification of patients with ACS rather than general markers of inflammation.

Diabetes, Coronary Intervention, and Platelet Glycoprotein IIb/IIIa Blockade

Diabetes mellitus is associated with inferior outcome after percutaneous coronary intervention (PCI).1 Platelet glycoprotein IIb/IIIa (GP IIb/IIIa) inhibition is an important adjunctive therapy during PCI and may be particularly so in patients with diabetes mellitus.2 Platelet GP IIb/IIIa inhibitors are potent antithrombotic agents, and in several large-scale clinical trials with balloon angioplasty and coronary stenting, these agents have produced a consistent and marked reduction in both 30-day ischemic events and long-term (up to 1 to 3 years) mortality.3 In most cases, a greater magnitude of survival benefit with abciximab has been observed in patients with diabetes as compared with patients without diabetes.3–5 Furthermore, clinical risk stratification with diabetes and other variables reliably predicts abciximab benefit for late survival, thereby validating the important mortality benefits (nearly 3 lives saved per 100 patients treated) with abciximab use in high-risk patients during PCI.6 This large body of evidence has led to the widespread acceptance of platelet GP IIb/IIIa inhibitors to neutralize the excessive mortality associated with PCI among patients with diabetes as compared with patients without diabetes. See p 3627 The introduction of clopidogrel has changed the landscape of clinical outcomes in PCI. In patients with diabetes, clopidogrel has been shown to be superior to aspirin in reducing recurrent ischemic events.7 The use of preprocedural clopidogrel can attenuate the increase in C-reactive protein and other inflammatory markers after PCI, even in the presence of abciximab.8,9 Pretreatment with clopidogrel (300 to 600 mg) has been suggested to reduce ischemic events during PCI, and long-term (1 year) clopidogrel therapy has been shown to reduce long-term clinical events.10 Recently, the ISAR-REACT (Intracoronary Stenting and Antithrombotic Regimen-Rapid Early Action for Coronary Treatment) study found no benefit with abciximab therapy versus placebo in low- and intermediate-risk patients undergoing PCI who …

Breast adenocarcinoma cell adhesion to the vascular subendothelium in whole blood and under flow conditions: Effects of α v β 3 and α IIb β 3 antagonists

Tumour cell adhesion to vascular extracellular matrix (ECM), an important step of metastatic progression, is promoted by platelets. The aim of our study was to investigate, in whole blood under venous and arterial shear conditions, the respective role of tumour cell alphavbeta3 and platelet alphaIIbbeta3 integrins in MDA-MB-231 breast adenocarcinoma cell adhesion to human umbilical vein endothelial cell ECM. For that purpose, blood containing MDA-MB-231 cells was incubated with non-peptide antagonists specific for platelet alphaIIbbeta3 (lamifiban) or tumour cell alphavbeta3 (SB-273005). At 300 s(-1), each antagonist used alone did not modify tumour cell adhesion, whereas, at 1500 s(-1), tumour cell adhesion was decreased by 25% in presence of lamifiban indicating a role of platelet alphaIIbbeta3 at higher shear rate. However, a combination of SB-273005 and lamifiban, or c7E3 Fab (a potent inhibitor of both alphaIIbbeta3 and alphavbeta3) inhibited tumour cell adhesion by 40-45%, at either shear rate applied, indicating a cooperation between these two integrins in MDA-MB-231 cell adhesion to ECM, as well as the participation of other adhesive receptors on tumour cells and/or platelets. Thus, efficient anti-metastatic therapy should target multiple receptors on tumour cells and platelets.

Prognostic value of placental growth factor in patients with acute chest pain.

Experimental data suggest that placental growth factor (PlGF), a member of the vascular endothelial growth factor family, acts as a primary inflammatory instigator of atherosclerotic plaque instability and thus may be useful as a risk-predicting biomarker in patients with acute coronary syndromes (ACS). To determine whether blood levels of PlGF predict risk for death or nonfatal myocardial infarction in patients with acute chest pain. Measurement of PlGF levels as well as levels of markers of myocardial necrosis (troponin T [TnT]), platelet activation (soluble CD40 ligand [sCD40L]), and inflammation (high-sensitivity C-reactive protein [hsCRP]) in an inception cohort of 547 patients with angiographically validated ACS participating in the CAPTURE (c7E3 Fab Anti-Platelet Therapy in Unstable Refractory Angina) trial and in a heterogeneous cohort of 626 patients presenting with acute chest pain to an emergency department in Germany between December 1996 and March 1999. Risk for death or nonfatal myocardial infarction after 30 days. In patients with ACS, elevated PlGF levels (>27.0 ng/L; 40.8% of patients) indicated a markedly increased risk of events at 30 days (14.8% vs 4.9%; unadjusted hazard ratio [HR], 3.34; 95% confidence interval [CI], 1.79-6.24; P<.001). In a multivariable model, elevated levels of TnT (HR, 1.83; 95% CI, 1.05-3.86; P =.03), sCD40L (HR, 2.65; 95% CI, 1.41-4.99; P =.002), and PlGF (HR, 3.03; 95% CI, 1.54-5.95; P<.001) were independent predictors, while elevated hsCRP level was not (HR, 0.98; 95% CI, 0.53-1.98; P =.94). In patients with acute chest pain, elevated levels of PlGF predicted risk (21.2% vs 5.3%) (unadjusted: HR, 4.80; 95% CI, 2.81-8.21; P<.001; adjusted: HR, 3.00; 95% CI, 1.68-5.38; P<.001). Patients negative for all 3 markers (TnT, sCD40L, and PlGF) were at very low cardiac risk (7 days: no event; 30 days: 2.1% event rate). Plasma PlGF levels may be an independent biomarker of adverse outcome in patients with suspected ACS. A single initial measurement of plasma PlGF appears to extend the predictive and prognostic information gained from traditional inflammatory markers.

Major bleeding and severe thrombocytopenia after combined heparin and abciximab—c7E3 Fab therapy

Eur J Vasc Endovasc Surg 25, 85–87 (2003)

RhoA Sustains Integrin αIIbβ3Adhesion Contacts under High Shear

The small GTPase RhoA modulates the adhesive nature of many cell types; however, despite high levels of expression in platelets, there is currently limited evidence for an important role for this small GTPase in regulating platelet adhesion processes. In this study, we have examined the role of RhoA in regulating the adhesive function of the major platelet integrin, alpha(IIb)beta(3). Our studies demonstrate that activation of RhoA occurs as a general feature of platelet activation in response to soluble agonists (thrombin, ADP, collagen), immobilized matrices (von Willebrand factor (vWf), fibrinogen) and high shear stress. Blocking the ligand binding function of integrin alpha(IIb)beta(3), by pretreating platelets with c7E3 Fab, demonstrated the existence of integrin alpha(IIb)beta(3)-dependent and -independent mechanisms regulating RhoA activation. Inhibition of RhoA (C3 exoenzyme) or its downstream effector Rho kinase had no effect on integrin alpha(IIb)beta(3) activation induced by soluble agonists or adhesive substrates, however, both inhibitors reduced shear-dependent platelet adhesion on immobilized vWf and shear-induced platelet aggregation in suspension. Detailed analysis of the sequential adhesive steps required for stable platelet adhesion on a vWf matrix under shear conditions revealed that RhoA did not regulate platelet tethering to vWf or the initial formation of integrin alpha(IIb)beta(3) adhesion contacts but played a major role in sustaining stable platelet-matrix interactions. These studies define a critical role for RhoA in regulating the stability of integrin alpha(IIb)beta(3) adhesion contacts under conditions of high shear stress.

Thrombocytopenia associated with c7E3 Fab (abciximab).

Abciximab (c7E3 Fab) inhibits platelet aggregation and is used to prevent complications of percutaneous coronary intervention. Thrombocytopenia is an often-cited complication of abciximab. Pseudothrombocytopenia is due to ethylenediaminetetraacetate (EDTA)-activated platelet agglutination, resulting in a spuriously low platelet count. We have looked at both "true" and pseudothrombocytopenia after infusion of abciximab. Sixty-six patients receiving their first exposure to abciximab after an unstable coronary event/revascularization were eligible. All the patients received a bolus of c7E3 Fab followed by a continuous infusion. Platelets were monitored in all patients at 2, 4, 12, 24, and 48 h, and more frequently if required. The incidence of thrombocytopenia and acute severe thrombocytopenia (platelet count < or =20,000/microl) was evaluated. A peripheral blood smear was performed on all patients showing thrombocytopenia to evaluate for pseudothrombocytopenia. Seventeen (25.6%) developed thrombocytopenia and nine (13.6%) developed acute severe thrombocytopenia. However, 18 of these patients had pseudothrombocytopenia. The onset of true thrombocytopenia was at 4 h after the infusion, while pseudothrombocytopenia occurred at anytime during the first 24 h. Only two (3.03%) patients required platelet transfusions. No life-threatening hemorrhagic complications were recognized. Five of six subjects with true thrombocytopenia had positive laboratory findings of disseminated intravascular coagulation; however, none had an adverse outcome. Acute severe thrombocytopenia was noted to be a relatively benign adverse effect of abciximab. There is an increasing incidence of pseudothrombocytopenia in this subgroup of patients. It would be worthwhile examining a peripheral blood smear or collecting blood for platelet counts in a heparin-coated tube in order to exclude this phenomenon and thereby prevent inappropriate discontinuation of this drug.

Paradoxical Platelet Activation Was not Observed on Dissociation of Abciximab from GPIIb-IIIa Complexes

The ability of abciximab to bind and dissociate from platelets raises the question of the conformational state of GPIIb-IIIa complexes losing abciximab and the risk of paradoxical drug-induced platelet activation. Platelets incubated with abciximab and mixed in vitro with c7E3 Fab-free platelets lost the drug to the new platelets giving a single platelet population with a unimodal abciximab distribution within 17 h. Prelabeling the receiving platelets with phycoerythrin-labeled anti-GPIb monoclonal antibody (MoAb), permitted their identification by flow cytometry. Binding of PAC-1 and AP6, two MoAbs specific for activated GPIIb-IIIa, was then assessed to both losing and receiving platelet populations during transfer of abciximab. The subpopulation losing c7E3 Fab failed to show increased binding of these MoAbs. However, PAC-1 binding increased in both subpopulations after addition of ADP. Thus GPIIb-IIIa complexes are not in an activated state after dissociation of abciximab unless there is an additional source of activation.

Differential Effects of c7E3 Fab on Thrombus Formation and rt-PA-Mediated Thrombolysis Under Flow Conditions

Although the Fab fragment of the mouse–human chimeric anti-α IIbβ 3 (GP IIb/IIIa) monoclonal antibody (MoAb) c7E3 facilitates recombinant tissue-type plasminogen activator (rt-PA)-mediated thrombolysis, it is not clear whether this is due to inhibition of new clot formation and/or a direct effect on the lysis rate. We employed an in vitro flow (re)circulation model to investigate how c7E3 Fab affected (a) platelet adhesion to clotted fibrin substrates under laminar flow at wall shear rates of 100 or 500 s −1 and (b) rt-PA-induced lysis of preformed mural platelet–fibrin substrates at 500 s −1. c7E3 Fab dose-dependently (0.5–5 μg/ml) inhibited platelet adhesion from flowing whole blood onto fibrin substrates (∼14 μm thick) at each wall shear rate. When at 5 min after the onset of flow, c7E3 Fab (0.1–10 μg/ml) and rt-PA (1 μg/ml) were coinjected in flowing blood, it was found that modest fibrinolysis caused major platelet release from fibrin substrates and there was no difference in the lysis rate in the presence of rt-PA+c7E3 Fab compared to rt-PA alone. Platelet pretreatment with c7E3 Fab (10 μg/ml) had no effect on the lysis rate of thin (∼40 μm), and slightly delayed the lysis rate of thick (<250 μm), platelet–fibrin substrates containing evenly dispersed platelets (10 9/ml). When the platelets within thick platelet–fibrin substrates were organized in platelet-rich regions (“residual thrombi”), these substrates followed a nonuniform lysis pattern, where fibrin between the thrombi lysed first and the residual thrombi lysed at a slower rate. Platelet pretreatment with c7E3 Fab (10 μg/ml) abolished the formation of the lytic-resistant residual thrombi and the associated platelet-protected fibrin zones. Hence, treatment with c7E3 Fab has no direct effect on the rate of rt-PA-mediated lysis, but is expected to block platelet–fibrin interactions that lead to clot retraction, thus maintaining a fibrin architecture that is more susceptible to lysis.

Effects on thrombin generation of the platelet glycoprotein IIb/IIIa inhibitors abciximab versus tirofiban during coronary intervention

Glycoprotein (GP) IIb/IIIa receptor blockers have been shown to reduce adverse events in randomized clinical trials. 1‐ 4 Not only will these agents reduce platelet aggregation but, as activated platelets facilitate thrombin formation, these agents should also possess effects on reducing thrombin generation.5 Experimental and in vivo studies indicate that abciximab alone or in combination with standard-dose intravenous heparin decrease thrombin generation and fibrin formation. 6‐8 Furthermore, in a thrombin generation assay triggered by tissue factor, Reverter et al 9 found that c7E 3Fab (abciximab) through both GP Ilb/IIIa blockade and a v b3 blockade (vitronectin receptor) inhibited tissue factor-induced thrombin generation. 9 On the other hand, the small molecule inhibitors of the GP IIb/IIIa receptor are specific for this receptor alone and do not interact with the vitronectin receptor. Their effects in vivo on thrombin generation in human subjects have not been well studied. In this paper, we compared these antithrombin effects of tirofiban and heparin compared with abciximab and heparin on the activated clotting time (ACT), prothrombin fragment F1.2, and GP IIb/IIIa platelet receptor occupancy using a standardized protocol.

GP IIb/IIIa receptor antagonists in unstable angina: troponin level-based patient selection

Troponins T and I are biochemical markers for thrombotic microembolization and minor myocardial injury and have proven to be sensitive prognostic indicators in patients with unstable angina. An analysis of data from the c7E3 Fab Antiplatelet Therapy in Unstable Refractory Angina (CAPTURE) trial has shown that troponin-negative patients had a low incidence of cardiac events and did not benefit from glycoprotein (GP) IIb/IIIa receptor blockade. Abciximab significantly reduced both the short- and long-term risks of death or acute myocardial infarction in patients with baseline elevations in troponin. This has been confirmed in retrospective analyses of other trials. The combination of pre-treatment with a GP IIb/IIIa receptor antagonist with early invasive management was shown to provide the best outcome in the Thrombolysis and Counterpulsation to Improve Cardiogenic Shock Survival (TACTICS) study. Troponin measurements represent a practical and simple tool for risk stratifying patients with unstable angina and selecting those most likely to benefit from potent platelet inhibitor therapy.

7E3 F(ab’)2, an Effective Antagonist of Rat αIIbβ3 and αvβ3, Blocks In Vivo Thrombus Formation and In Vitro Angiogenesis

Abciximab (c7E3 Fab, ReoPro) blocks GPIIb/IIIa and alphavbeta3 and inhibits thrombotic and proliferative events only in humans and non-human primates. The bivalent F(ab')2 fragment is an effective anti-thrombotic agent in canine models. In the present study, 7E3 F(ab')2 was also found to bind to rat GPIIb/IIIa (KD = 27 +/- 4 microg/mL) and alphavbeta3 (KD = 9 +/- 8 microg/mL), to block in vitro rat platelet aggregation (IC50 = 16 +/- 6 microg/mL), and to inhibit alphavbeta3-mediated microvessel sprout formation in a rat aortic ring assay. Following administration of 7E3 F(ab')2 (4 mg/kg) to rats, platelet aggregation was completely blocked for up to 6 h and thrombus formation in response to a rat abdominal aorta double crush injury was prevented. Effective chronic dosing was achieved with 6 mg/kg daily I.P. injections. In vitro mixing experiments indicated that 7E3 F(ab')2 redistributed to unlabeled platelets in 2 h. Ex vivo, 7E3 F(ab')2 was detected on platelets for up to 4 days after a single 4-mg/kg injection. These data suggest that 7E3 F(ab')2 may be a useful agent to study the effects of GPIIb/IIIa and alphavbeta3 blockade in rat models of thrombosis and vascular disease.

Inhibition of vascular smooth muscle cell adhesion and migration by c7E3 Fab (abciximab): a possible mechanism for influencing restenosis.

Brief intravenous administration of chimeric antibody c7E3 Fab during coronary angioplasty has been shown in some studies to provide long term protection against coronary events. Smooth muscle cell (SMC) adhesion and migration are key initial steps in the development of restenosis. The purpose of this study was to investigate the effect of c7E3 Fab on adhesion and migration of SMC to the extracellular matrix (ECM) proteins osteopontin (Opn) and vitronectin (Vn). Adhesion of human vascular SMCs to ECM proteins was quantified using a CyQUANT assay kit. Migration of SMCs to Vn, Opn and PDGF was studied using a modified Boyden's chamber migration assay. Integrin expression was determined by immunoprecipitation. c7E3 Fab reduced SMC adhesion on Vn and Opn to 69.2+/-3.3% (P<0.001) and 52.5+/-4.8% (P<0.001) respectively, compared to adhesion without antibody present. This reduction was the same as that for anti-alpha(v)beta(3) integrin antibody LM609 (P=0.5). The combination of anti-alpha(v)beta(5) integrin antibody and c7E3 Fab had a greater effect than either antibody alone (P<0.001). c7E3 Fab reduced SMC migration to Vn and Opn to 51.6+/-8.9% (P<0.001) and 20.3+/-6.1% (P<0.001) respectively, compared to migration in the absence of antibodies. Again, similar results were seen with LM609. PDGF-induced SMC migration was also inhibited by c7E3 Fab (P=0.004) and LM609 (P=0.001), but to much less an extent. The migration SMCs from a culture found not to express the alpha(v)beta(3) integrin was unaffected by these antibodies, strengthening the argument that c7E3 Fab inhibits SMC function via this integrin. c7E3 Fab inhibits the adhesion and migration of SMCs via the alpha(v)beta(3) integrin. The inhibition, however, is partial, and varied depending on type of ECM protein and alpha(v)beta(3) integrin expression. Some of the clinical benefits of c7E3 Fab may be due to its effect on SMCs.

Effects of the glycoprotein IIb/IIIa receptor antagonist c7E3 Fab and anticoagulants on platelet aggregation and thrombin potential under high coagulant challenge in vitro.

The present study was performed to investigate the combined effects of the platelet glycoprotein IIb/IIIa receptor antagonist c7E3 Fab (abciximab) and the anticoagulants unfractionated heparin (UH), low molecular weight heparin (LMWH), and recombinant hirudin (rH) on platelet aggregation and thrombin generation under high coagulant challenge by extrinsic activation of platelet-rich plasma. Platelet aggregation and thrombin generation were assessed simultaneously in the presence of different concentrations of abciximab and anticoagulants. Increasing concentrations of abciximab resulted in a dose-dependent anti-aggregating effect with a maximum at 20 microg/ml. Doses of 5, 10, and 20 microg/ml abciximab prolonged the lag phase until the onset of platelet aggregation, but this effect was independent of the dosage used. Abciximab had no influence on the thrombin potential under our high coagulant challenge. UH, LMWH, and rH showed a dose-dependent prolongation of the lag phase until the onset of platelet aggregation and decreased the thrombin potential. Addition of anticoagulants did not contribute to further inhibition of platelet aggregation in the presence of abciximab, but the combination of abciximab and anticoagulants exhibited an additive effect on prolongation of the lag phase until the onset of platelet aggregation. Addition of abciximab to anticoagulants did not result in further decrease of the thrombin potential. Our study demonstrates the respective specific effects of abciximab and anticoagulants on platelet aggregation and thrombin potential under high coagulant challenge, and also an additive effect of abciximab and the anticoagulants UH, LMWH, and rH on the lag phase until the onset of platelet aggregation.